Ultrahigh-flux (>190,000 L·m⁻²h⁻¹) separation of oil and water by a robust and durable Cu(OH)₂ nanoneedles mesh with inverse wettability

Single-stage oil/water separation membranes usually suffer from weak chemical stability, susceptible mechanical damage and relatively low permeating flux, and the sophisticated preparation processes also limit their massive utilization. In this work, Cu(OH)₂ nanoneedles coated copper mesh (CM) is prepared by simple and eco-friendly anodic oxidation at a current density of 4 mA/cm² for 6 min, which is the most efficient route reported so far. The mesh exhibits outstanding superhydrophilicity and underwater superoleophobicity towards various oils with contact angles up to 164.9°, achieving superior oil/water separation efficiency of above 99.5% and ultrahigh permeating flux of 191 160 L·m⁻²h⁻¹ solely driven by gravity. Impressively, the Cu(OH)₂/CM demonstrates excellent chemical stability and anti-fouling performance when exposed to acidic and strongly alkaline solutions, saturated NaCl solution and various organic solvents. High durability to withstand mechanical challenges, e.g. high-power sonication and sand abrasion, is experimentally confirmed owing to strong cohesional strength of Cu(OH)₂ nanoneedles on CM surface. Importantly, the Cu(OH)₂/CM exhibits favorable long-term recyclability with stable microstructure morphologies even after 50 cycles. These distinct advantages endow the Cu(OH)₂/CM to be an ideal candidate to efficiently separate oil pollutants from water. The oil/water separation mechanisms are proposed based on the concept of intrusion pressure.